Annoying bug in single point thread mill tool creation

[Muzzerboy]

I'm struggling to create a simple, single tooth thread mill tool. I have a SIMturn DX boring tool with the internal 3mm threading insert. This makes a fine thread mill but Fusion doesn't think it should be made easy. I need to mill an M16x2.0 internal thread and have the 3mm insert. 

When I try to define the tool in the tool library, I get an annoying shoulder on the insert if I specify the correct tool diameter. In this case, clearly I need that to be less than 14mm or so to fit in the bore - in fact it's 9.44mm at the point of the tool for this insert. The annoying shoulder bug / artefact only appears when the tool diameter is reduced below 15-20mm, depending on the pitch you specify. When I specify 3mm and a diameter of 9.44mm, the resulting profile is nothing like a 3mm tooth.

Here's the correct 3mm wide tooth on a large diameter tool:

Reducing the diameter to 15mm causes the tooth width to reduce and the Annoying Shoulder starts to appear:

Here's the tool I'm trying to create, with a 3mm tooth width and 9.44mm diameter at the tip. I'm actually getting something like 1.3mm and a shoulder.

The 3 attachments show what happens when you reduce the diameter of the tool, leaving the pitch, flute length and  shoulder length the same (3mm in my case). Once you get down below something like 16-17mm diameter, the Annoying Shoulder appears and by the time you have reduced the diameter to 9.44mm, the effect is quite severe.

You might think it's not an issue but the profile of the cutting edges are completely wrong. Instead of a 3mm wide tooth, I get a ~1.3mm wide tooth and a ~1.7mm wide Annoying Shoulder that I can't do anything with.

I'm guessing there's some mathematical expression going on under the tool dialog box that causes this.

Do I need to create a form tool to get around this or is it actually possible to use the thread mill feature to create a....thread mill? Hopefully somebody will tell me I've made a dumb mistake and show me the simple solution.

I don't know how to attach a single tool but you can see the problem quickly if you create a thread mill tool with the dimensions shown (3mm pitch, 9mm diameter).

[Anonymous]

I doesn't seem to care what i put in shaft diameter, diameter stays the same.

[christopher.cooperVHK2N]

@Muzzerboy Thankyou for bringing this to our attention in such a detailed manner. I have added the details to a task that outlines the bug and will bring it up with the development team.

I am not sure if this is just a graphical bug or if it affects the code @Anonymous @seth.madore maybe able to advise you on a work around if it required.

Thanks

Chris

[seth.madore]

The code is going to be correct, it's "just" a graphical bug. However....

Are you doubling the diameter size? If you are using this in a mill, consider that the tool is spinning, thus whatever insert profile you are using will now become a "revolved" feature.

[Anonymous]

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@seth.madore wrote:

The code is going to be correct, it's "just" a graphical bug. However....

Are you doubling the diameter size? If you are using this in a mill, consider that the tool is spinning, thus whatever insert profile you are using will now become a "revolved" feature.

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He is using 9mm diameter, 3mm pitch, solid carbide, single tooth tool, would you then define it as 4.5mm diameter?

It's not really my domain but it doesn't seem right.

[Muzzerboy]

Sorry, been away with work. Yes, the 9mm is the diameter of the locus of the tip.

It's difficult to know what offset etc to set for the cutter when I set up the operation. The simulation / preview features don't help much if the tool profile isn't right. I prefer an analytical approach rather than trial and error, so this bug thing is an issue for me.

As a workaround, should try to define a profile cutter, rather than try to make the thread mill feature behave? For now, I'm happy to help to bottom this out but I'm also trying to mill an internal thread in a part that is otherwise almost complete.

[Muzzerboy · Accepted solution]

Time and tide waits for no man, so I made a profile tool instead. This still wasn't a walk in the park, as it doesn't seem to be obvious how you'd edit a profile tool after you've made it. You can edit the originating sketch but it doesn't seem to get pulled through unless I missed something. I ended up making several tools, finally ending up with something that worked, taking the dimensions from the Simturn datasheets for the boring bar and the threading insert.

You need to select the smaller diameter of an internal thread (safest to avoid modelled threads and important to dimension the bore with the correct root diameter). The pitch diameter offset isn't well explained, figuring out which specific part of the cylindrical face the reference point aligns to is a mystery (presumably zero degrees on the top surface) and the end result didn't work out quite as the calculations appeared to suggest it would. However, I got the thread to the right fit after a couple of adjustments. Not a fan of trial and error, so I can't help thinking some more work is required here, not least explaining what is happening under the hood.

[seth.madore]

@Anonymous a form tool is drawn up the same way you would for drawing a lathe turned part; draw the radial features and any required lines and arcs, and then perform a revolve. In this case, the Form Tool tool will create the revolve behind the scenes.

[Anonymous]

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@seth.madore wrote:

@Anonymous a form tool is drawn up the same way you would for drawing a lathe turned part; draw the radial features and any required lines and arcs, and then perform a revolve. In this case, the Form Tool tool will create the revolve behind the scenes.

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I think there is a miscommunication here, I know how to create form tool but before OP "discovered" it as an alternative, he was trying to define tool from library as 9 mm diameter and 3 mm pitch.

I only commented about shank size in tool image not reflecting change in diameter even though I entered different number.

So, I think things got a little confused in transition to form tool.